Such an assembly is known from French patent 2 649 185 A1.
The known assembly is designed for use as a headlamp in motor vehicles. The assembly in addition comprises an annular lamp carrier which has a concave, spherical surface and facing away therefrom a flat surface. The lamp carrier is immovably fastened against the mounting surface with its spherical surface.
The electric lamp comprises a lamp cap having a flat circumferential collar. The lamp is held in the annular lamp carrier with its flat collar against the flat surface.
The known assembly has for its object to render it possible for the electric element to be arranged coaxially with the reflector inside the latter while its center coincides with the optical center of the reflector. For realizing such an arrangement, the electric element must be aligned when a lamp is inserted and whenever a lamp is replaced by a new one. If the electric element in the lamp has a tilted position, the lamp carrier can be loosed from the mounting surface, after which the lamp carrier can be shifted over the mounting surface so as to be tilted relative to the optical axis. The electric element can thereby be brought into a position parallel to the optical axis. Subsequently, the collar of the lamp cap can be shifted in two directions over the flat surface in order to let the electric element cover the optical center.
It is often not possible for the user to carry out these alignment steps since they require a high degree of expertise and/or special equipment.
For practical applications, the known assembly has the drawback that a non-expert user is capable of making a greater positioning error by the lateral displacement possibility of the lamp alone, with the flat collar moving over the flat surface of the lamp carrier, than if the lamp carrier were to be just large enough to accommodate the lamp cap. For practical purposes the construction of the known assembly is equivalent to that of a reflector having a fixed lamp opening in which a lamp is laterally displaceable. The construction of the known assembly is accordingly of a totally insufficient accuracy for use in an optical system.
A lamp opening which is just large enough to accommodate the lamp cap does not offer a sufficiently accurate positioning of the electric element in the reflector either. This is caused by the spread in the dimensions of the lamp opening and of the lamp cap which occurs in mass manufacture.
German DE-1 472 529-A discloses an assembly in which the reflector has a lamp opening bounded by a conical wall and the lamp cap has a conical surface, so that the position of the electric element inside the reflector can be three-dimensionally determined.
This latter construction, however, is not sufficiently accurate for various applications because the lamp opening and the lamp cap cannot be manufactured to sufficiently narrow tolerances. Moreover, the accuracy of the position of the electric element along the optical axis is greatest in this case when the cones have the greatest possible apex angle, but the position transverse to the axis is most accurately determined when the cones have a small apex angle, so it is only possible to choose an apex angle which is a compromise. Aspects which then come into play are how securely the lamp cap is pressed into the lamp opening and to what extent a skew position of the lamp cap is prevented.
U.S. Pat. No. 4,061,912 discloses an assembly which is similar to the assembly described in the opening paragraph. In this case, however, the center of curvature of the mounting surface does not lie in the optical center of the reflector but in its lamp opening, and the optical center does not coincide with the electric element. This known assembly is designed for use in a luminaire for theater illumination. It envisions to provide the possibility of changing the position of the electric element, an incandescent body, in the reflector during lamp operation so as to change the shape of the generated light beam. To this end, a lampholder in which the lamp cap of the lamp is accommodated is fastened to the mounting surface with lateral shifting possibility. This renders the same displacement of the incandescent body within the reflector possible as would be possible if the lamp were suspended in a ball joint in the lamp opening. Moreover, the lampholder may be brought to a varying distance from the mounting surface, so that the lamp can project more or less deeply into the reflector. The adjustment possibility of the lampholder is necessary not only for producing light beams of various shapes, but also because the incandescent body assumes a random position relative to the lamp cap, and thus relative to the lampholder. The advantage of this construction with the center of curvature in the lamp opening is that major lateral displacements of the lampholder, and thus of the lamp cap and of the incandescent body, are possible without the lamp opening having to be substantially greater than the diameter of the lamp vessel.
An adjustment possibility for the location of the electric element is only possible in those applications in which an exact position of the electric element is of no importance for obtaining a light beam of a certain kind.
For many applications in optical systems, however, it is necessary for the electric element of a lamp to take up a predetermined position inside the reflector with a high accuracy. It is often not possible then to allow the user to find this location because of the high skill and/or special aids necessary for this. This electric element in these cases must take up a predetermined position relative to a lamp cap, and the lamp cap must automatically assume a predetermined position relative to the reflector, so that the electric element will be in the correct position inside the reflector when the lamp is inserted.